By Kris Osborn, Warrior
As one of the most famous fighter jets ever not-to-exist, the experimental F-15 Silent Eagle variant presents somewhat of a paradox, because while it ultimately seemed to fall short of the mark in relation to its initial goal, the project did generate technologies and developmental strategies woven into the now famous F-15EX.
Regarded as a “4th-Generation Plus” kind of breakthrough fighter jet, the F-15EX does incorporate a number of 5th-gen like attributes and does appear to lower the radar signature of the famous fighter. Which attributes in particular may have emerged from the F-15SE? Perhaps of equal significance, why were the ambitious efforts to build and present the F-15 Silent Eagle ultimately unsuccessful?
The intent of the Boeing F-15SE, which emerged in 2009, was primarily to present the jet to allied foreign customers, yet the aircraft did not exist and many of its innovations were instead directed to the F-15EX advanced variants.
The shape of the F-15SE does look slightly stealthier than preceding variants as it incorporated a somewhat more rounded wing-body kind of configuration and was built with a new conformal weapons bay and conformal fuel tanks to reduce radar signature. The advantage with this was that it improved stealth properties while also greatly expanding the aircraft’s weapons carrying capacity. The Silent Eagle was also built with “canted vertical stabilizers,” structures also intended to reduce radar signature. “Canted” or “angled” stabilizers are intended to deflect electromagnetic pings “away” from airborne radar.
Using two stabilizers enables the structures to be shorter, a design method used to lower the overall vertical height of the aircraft. While angled stabilizers may “deflect” radar return signals to some degree, they are “protruding” structures likely to generate some kind of rendering, as opposed to a fully horizontal flying wing stealth bomber kind of configuration. The F-15SE was also reportedly engineered with extensive radar-absorbing materials designed to decrease any return electromagnetic return signal, a technological method used in most stealth platforms.
“Not so Silent Eagle?”
However, despite being arguably stealthier than some of the F-15 variants which preceded it, the F-15SE looks like it was a long way from the kind of “F-22” and “F-35”-like stealth effectiveness for several key reasons. Yes the aircraft was built with an internal weapons bay, yet extra pylon “hardpoints” were added beneath the wings. This of course increases weapons capacity for attack but also adds protruding, external “angled” structures to the body of the aircraft, shapes, edges and contours likely to generate a much larger radar return signal or rendering to ground and air-based enemy radar systems.
A quick look at the configuration of the Silent Eagle aircraft seems to indicate that, arguably, the aircraft is not particularly stealthy when compared with 5th-gen aircraft. An F-22, for example, has what appears to be a completely smooth exterior structure without protruding shapes. Its inlets are built into the fuselage to a much greater degree, whereas the inlets on the F-15SE look sharply angled and completely external to the body of the aircraft. Both the F-22 and the F-35 can operate with smooth bolts and seams and a internal weapons bay designed to ensure a smoother, flatter configuration.
Influence on F-15EX
Sure enough, the body of the F-15EX does mirror the more horizontal blended wing-body type of smoother fuselage used in the Silent Eagle, and the wings do connect to the body of the aircraft with smooth, rounded horizontal structures “flattening” the aircraft. This is something which of course increases stealth characteristics and reduces radar cross-section. The initial F-15EX aircraft do not have conformal fuel tanks, as they are optimized for aerial agility as opposed to a longer-range kind of “missile truck” configuration. However, conformal fuel tanks can also be added to the aircraft. This being said, a close look at the mid-body section of the F-15EX does slightly resemble the body structure of an F-22, particularly with its dual engine configuration.